I. Field of the Invention:
The present invention is directed to adhesive compositions containing rubbery block copolymers which adhesives are improved with respect to their heat resistance by the addition thereto of specific polyamide resins.
II. Brief Description of the Prior Art
Adhesive compositions based on elastomeric block copolymers have long been known in the art and are represented by U.S. Pat. Nos. 3,239,478; 3,932,327; 3,427,269; 3,700,633; 3,753,936; 3,837,994; 4,136,699; 4,212,910, and 4,259,220 among others. While these adhesives are suitable for many purposes, they may lack a combination of critical properties which limit their broader commercial utilization. In particular, some adhesive compositions are deficient in adhesive characteristics at relatively high temperatures. For many purposes, it is desirable that an adhesive function satisfactorily not only at room temperature but at substantially higher temperatures, on the order of 80.degree.-150.degree. F. In other situations, wherein the intended use of the adhesive is for applications to surfaces containing substantial amounts of plasticizer, many of these elastomeric block copolymer adhesives are deficient and do not have adequate resistance to plasticizers, particularly when exposed to elevated temperatures.
Attempts to improve heat resistance and plasticizer resistance of these adhesives have been made by including conventional tackifying resins in the formulations; however, this approach has proven inadequate. Other attempts to overcome these problems are taught in U.S. Pat. Nos. 3,935,338 and 3,917,607 wherein specific resins, such as coumarone-indene resins, which serve to reinforce the end blocks of the block copolymer resins are employed. Not only did the use of the latter types of resins fail to provide sufficient heat resistance for many end uses, but their use also resulted in an appreciable reduction in the tack of the adhesive composition itself.